Heat exchanger

ABSTRACT

The heat exchanger is made economically by using thermoplastic sheets with hollow tubes and spacers between the sheets and fusing the edges of the sheets together to form an integral housing. Preferably, the heat exchanger is an opposed-flow heat-exchanger giving improved heat-transfer efficiency.

This patent application is a division of patent application Ser. No.09/829,772, filed Apr. 10, 2001, which is a continuation-in-part of U.S.patent application Ser. No. 09/188,729, filed Nov. 9, 1998, now U.S.Pat. No. 6,176,305, and Ser. No. 09/579,739 filed May 26, 2000.

This invention relates to ventilating systems and methods usingheat-exchangers for energy recovery, and to heat exchangers, especiallyexchangers suitable for use in such systems, and to methods forfabricating heat exchangers.

The ventilating systems of the above-identified patent applicationsrepresent significant improvements over prior ventilating systems.Nonetheless, further improvements are desirable, and it is an object ofthis invention to provide them.

One embodiment of the ventilating system of the above patentapplications uses evaporative cooling to cool exhaust air exiting abuilding or other conditioned space. Although the evaporative coolingfeature significantly enhances the efficiency of cooling the conditionedspace, even greater cooling is highly desirable, as long as power andequipment costs are not increased excessively.

Prior energy-recovery ventilating systems and others using isolatingheat-exchangers, that is, heat-exchangers which isolate the gas flowsfrom one another, often suffer from the effects of leakage in the heatexchanger. This leakage causes undesired mixing of the two gases fromone another. In a ventilating system, this can mean that the staleexhaust air mixes with the incoming fresh air, and leads to reduced airquality and even contamination of the incoming fresh air.

A third problem occurs with the preferred heat exchanger used in myabove-described prior system. That heat-exchanger is made out ofextruded thermoplastic panels composed of side-by-side plastic tubes.The heat-exchanger is admirably suited to use with evaporative coolingequipment because mold and other such nemeses do not adhere strongly tothe heat-exchanger surfaces, and can be removed relatively easily. Also,the heat-exchanger is relatively inexpensive to build and lasts muchlonger than most metallic heat-exchangers.

A problem with such heat-exchangers is that most are relatively lessefficient in the transfer of heat than they could be.

Another problem is that such prior heat-exchangers usually requirerelatively expensive housings, often made of sheet-metal.

A further problem is that such prior heat-exchangers usually areassembled using hand labor, and thus are more time-consuming andexpensive to make than they need be.

In accordance with the present invention, the foregoing problems aresolved or alleviated by the provisions of a ventilating system andmethod which includes evaporative cooling of the exhaust air before itenters a heat exchanger to cool incoming fresh outside air. A suctionfan pulls exhaust air through the heat exchanger and, in combinationwith a flow restrictor, reduces the pressure on the exhaust air andaugments the evaporative cooling.

Preferably, another fan is used to push outside air through theheat-exchanger and into the conditioned space.

The use of a pusher fan to force outside air through the heat exchangerensures that any leakage in the heat-exchanger results in outside airentering exhaust air and minimizing the chances of contamination byleaking exhaust air into the incoming fresh air.

The heat exchanger is made economically by die-forming cavities inrelatively thick thermo-plastic sheets, interleaving them with otherthermo-plastic sheets having separate gas flow conduit structures, andsecuring the sheets together. Preferably, the heat-exchanger is anopposed-flow heat-exchanger giving improved heat-transfer efficiency.

In one embodiment, some or all of the sheets are panels of parallel,side-by-side thermoplastic tubes.

In one specific embodiment, the tubes in every other sheet are leftintact and serve as conduits for one gas, such as outside air, while theother sheets are indented to form separate conduits for another gas,such as exhaust air.

In another specific embodiment, the sheets indented to form gas flowpassages are panels made of expanded thermoplastic materials.

In a further specific embodiment, all of the panels have gas flowconduits formed by indenting the sheets.

Preferably, the outside edges of the sheets stacked together arehot-compressed, with a heated roller, e.g. to melt the plastic of theedges to form a relatively thick outer wall which is strong and helpsavoid the cost of a metal housing for the heat-exchanger. Flame singeingis used to fuse the ends of gas flow conduits together.

The sheets are secured together, broad-face to broad-face, either withsilicone adhesive, or preferably, by heat-singeing at least one broadsurface of one of the sheets to make it tacky before another sheet ispressed against the tacky surface to adhere the sheets together.

Vanes are die-formed in some of the gas flow passages to increaseturbulence and heat-transfer efficiency.

Die forming can be done with heated or cool dies, depending upon thetype of panel being used and its condition—whether hot and soft or cooland hard, for example.

The foregoing and other objects and advantages of the invention will beset forth in or apparent from the following description and drawings.

FIG. 1 is a perspective view of a heat-exchanger constructed inaccordance with the present invention;

FIGS. 2, 3 and 4 are side-elevation views of sheets or panels used tomake the heat-exchanger of FIG. 1;

FIGS. 5, 6, and 7 are cross-sectional views, partially broken-away,showing plural adjacent panels of heat-exchangers using the panels ofFIGS. 2, 3 and 4, and are taken at the locations indicated by the lines5-5, 6-6 and 7-7, respectively;

FIGS. 8, 9, 10 and 11 are perspective and cross-sectionalpartially-schematic views illustrating equipment and steps used in themanufacture of the heat-exchanger of FIG. 1;

FIG. 12 is an elevation view, partially schematic, showing a ventilatingsystem of the present invention; and

FIG. 13 is a cross-sectional view of a portion of an alternative panelused in the invention.

HEAT EXCHANGER

FIG. 1 is a perspective view of one embodiment of the heat-exchanger 20of the present invention.

The heat-exchanger 20 has opposed broad side walls 22, and top andbottom walls 24 and 26.

The heat-exchanger has an upper angular extension 28 defining an upperinlet/outlet 30, and a lower angular extension 32 defining a lowerinlet/outlet 34 connected internally to the upper inlet/outlet 30. Theinlet/outlets 30 and 34 and the internal passageways (not visible inFIG. 1) interconnecting them form a first gas flow conduit.

A second gas flow conduit is formed by inlet/outlets 36 and 38 at theright and left ends of the heat-exchanger, and internal passageways (notvisible in FIG. 1) interconnecting them.

Each of the various inlet/outlets 30, 34, 36 and 38 is capable of beingused either as an inlet or outlet for the flow of gases through theheat-exchanger.

As it will be explained in detail below, the two gas flow conduits areconstructed to be parallel to one another over a substantial portion oftheir lengths so as to produce counter-flow heat exchange when the gasesflow in opposite directions.

Panel Construction

The heat-exchanger 20 is made of a plurality of vertical panels orsheets 40, 42 interleaved with and secured to one another preferably inalternating sequence.

FIG. 2 is a side elevation view of one of the panels 40, and FIG. 3 is asimilar view of one of the panels 42.

The panels 40 and 42 are cut to have relatively long, straight parallelupper and lower edges with upper and lower angular extensions 44 and 46,and 63 and 65, respectively. The extensions are of the same size andshape so as to form the extensions 28 and 32 (FIG. 1) when the panelsare assembled together.

Preferably, both panels 40 and 42 are made of “sign-board” material,whose construction is shown in cross-section in FIG. 5.

As it is shown in FIG. 5, each panel 40 has relatively thin opposedoutside walls 54 and 56 with broad surfaces, and elongated integraltubes 53 of rectangular or square cross-section formed between two walls54 and 56. The panels are believed to be extruded from a thermoplasticmaterial such as polypropylene, polyethylene or polystyrene. Sign-boardmaterial typically is used as relatively lightweight, strong andinexpensive material for making signs or displays.

The structure of each panel 42 is substantially the same as thestructure of panel 40, and consists of outside walls 45 and 47 and tubes43. The panels may be thicker than panels 40, and the tubes 43 larger incross-sectional area than the tubes 52, so as to facilitate the flowconduit formation process.

As it is shown in FIGS. 3 and 5, the broad surfaces 45 and 47 of eachpanel 42 are indented in selected areas to form a pair of gas flowcavities 66. Preferably, the indentations are made by means of dies suchas the dies 136 and 138 shown in FIG. 11. The dies preferably are heatedin order to permanently deform the panel material.

When the panels 40 and 42 and assembled together with broad surfacescontacting one another, as shown in FIG. 5, gas flow passageways orconduits 67 and 69 are formed. Heat is transferred between the gas inconduits 67 and 69 and a single-thickness wall 56 of each adjacent panel40. This is an advantage over prior heat exchangers in which heat istransferred through multiple wall thicknesses.

As it is shown in FIG. 5, the indentations compress the internal wallsof the tubes together to form a two-ply wall 84 in the center of thepanel 42, with ribs 86 extending outwardly at the locations of thecompressed internal walls.

Preferably, vanes 76 (see FIG. 3) are formed in the gas flow cavities 66by the provision of cavities in the dies 13 and 138 (FIG. 11), which hasthe effect of leaving the panel material uncompressed and projectingoutwardly from the two-ply wall 84. The vanes 76 are arranged to serveas baffles to ensure the turbulent flow of gas along sinuous paths 80through the conduits 67 and 69, thus increasing the heat transferefficiency of the heat-exchanger.

Optional guide and support vanes 82 and 83 (FIG. 3) are formed by thesame process as the vanes 76 to divide the inlet section of each cavity66 into the passageways 72 and 74. The vanes 82 and 83 help to directthe flow of air through the conduits 67 and 69 first horizontally, fromright to left, as shown in FIG. 3, and then outwardly and downwardlythrough the outlet passageways 72 and 74.

The vanes 72, 74, 76, 82 and 83 also help to support the adjacentportions of panels 40 to maintain a constant spacing of the panels fromone another over the relatively broad span of the inlet and outletopenings.

An alternative panel construction 88 is shown in FIG. 4.

Panel 88 is an alternative to the panel 40 for conducting the gas flowfrom one end 38 (FIG. 1) to the opposite end 36.

Panel 88 has one or more indentations 94 with vanes 96, 102 and 104formed by the same process as the vanes 76. The dashed lines 97 indicatethe locations of rows of added vanes 96, which are not shown in FIG. 4for the sake of simplification of the drawings.

The vanes 102 and 104 are provided in order to support the adjacentpanels in the heat-exchanger, and to guide gases into and out of theflow passages of the heat-exchanger.

FIG. 7 shows the cross-sectional shape of one of the vanes 96.

The advantage of the panel 88 over the panel 40 is that the gas flowthrough the conduits is turbulent, thus further increasing theheat-transfer efficiency of the heat-exchanger.

Although it is preferred that the gas flow cavities in the panels beformed by indenting both broad side walls of the panels to form acentral two-ply web 84 as shown in FIG. 5, alternatively, the panels canbe indented from only one side to form the gas flow cavity 94.

FIG. 6 is a cross-sectional view taken along line 6-6 of FIG. 4 showingthis alternative construction. The panel which is indented has broadside walls 54 and 56 with tubes 52. The panel is heat-compressed to forma gas flow passageway in the area 112, and a two-ply wall 113 withridges 114 at the locations of the compressed inner walls.

Heat is transferred between the gas in the conduit 112 and that flowingin the tubes 52 of the adjacent panels 40. Although heat is transferredthrough only one wall thickness in the case of the wall 56, heat mustflow through the two-ply wall 113 and wall 54, when being transferredbetween conduit 112 and the right-hand panel conduits 52 shown in FIG.6.

This potential reduction in heat transfer efficiency, as compared withthe FIG. 5 embodiment, can be acceptable as a compromise to avoid havingto make two sets of heat-forming dies or heat-forming both sides of thepanels in separate steps using the same dies, if the extra die cost isavoided by using the same dies to form both sides of one panel.

The heat transfer reduction can be minimized by reducing the internaland external wall thickness of the panels 88, and by removingsubstantial sections of the two-ply wall 113 at many locations (e.g.115—see FIG. 4), in the panel shaping process.

The panels 40 utilize the tubes 52, which extend the whole length of thepanel, as gas flow conduits. However, the panels 42 and 88 do not usethe tubes to conduct gas. Instead, the panels are merely used aslow-cost thermoplastic sheet material from which to form gas flowconduits. It is possible to use other sheet materials instead for thestarting sheets for forming the panels 42 and 88.

For example, it is believed that sheets of expanded thermoplasticmaterials, such as polypropylene, polyethylene or polystyrene can beused instead of the “sign-board” material. Such sheet materials arewidely used as insulating panels in home construction, as flotationmaterials for floating docks, etc.

FIG. 13 is a broken-away cross-section of a panel of expandedthermoplastic material 117 compressed at 119 to form gas flow cavities121 and 123. This construction can be easier and less expensive to makethan that using sign-board as the starting material for all panels.

Similarly, other compressible and/or heat-formable sheets may beadvantageous to use as starting materials. For example, expanded orsolid thermo-plastic sheets, still hot after being formed, can bestamped or molded rapidly to provide the desired gas flow cavitieswithout the heating of dies. Some materials may be subject to permanentdeformation by the use of cool dies alone. It also is within the scopeof the invention to use those materials as alternatives.

Assembly of Panels

The next step in making the heat-exchanger 20 after cutting and formingthe panels is to adhere the panels together, with broad surfacescontacting one another, in alternating sequence. That is, for example, apanel 40 forms one side wall 22 of the heat-exchanger, and a panel 42 issecured to it. The next panel is another panel 40, the next is anotherpanel 42, etc. The other side wall 22 of the heat-exchanger would beanother panel 40.

The panels are adhered to one another with silicone adhesive, or by useof the process partially illustrated in FIG. 10.

Referring to FIG. 10, several flaming jets 124 are pointed downwardlyfrom burner nozzles 126 fed with fuel (e.g., natural gas) from amanifold 132. The flames are played onto the upper surface of one of thepanels 40 while the panel is moved past the flames in the direction 134at a controlled speed so as to “singe” the upper surface 56 of the panel40. This slightly melts or softens the upper surface of the panel. Then,the next panel is placed on top of the first panel, either with orwithout singeing the surface which is to make contact with the firstpanel, and the panels are pressed together and allowed to cool to causethem to adhere.

This process then is repeated for each subsequent panel added to thestack until a pre-determined number of layers has been formed.

The panels can be held together by many other methods and structures.

For example, metal clamps can be formed out of metal angles and crossrods (not shown) clamping the panels together.

Another assembly method which is believed to be feasible, under somecircumstances, is to simply clamp the panels together temporarily untilthe edges of the panels are fused together, in the manner to bedescribed below, and then removing the clamps, with the fused edgesbeing sufficient to hold the panels together.

Edge Fusing

FIG. 8 shows the preferred method of forming the top and bottom walls 24and 26.

When the panels are stacked together, the edges are aligned with oneanother to form straight surfaces. Then, a heated roller 118 is pressedfirmly against the upper edges 116 of the panels while the panels aremoved as indicated by the arrow 120. This progressively compresses andmelts the upper edges of the panels, and the melted plastic is rolled bythe roller to form a solid wall of melted plastic.

The panels then are turned over to use the same process to form theopposite wall.

Alternatively, a second heated roller (not shown), spaced verticallyfrom the roller 188 can be used simultaneously to form the top andbottom walls in one pass of the panels through the heated rollermechanism.

Many types of heated rollers can be used, such as ultrasonically-heatedrollers or rollers heated with electrical resistance heating.

The edges of the panels at the four inlet/outlets 30, 34, 36 and 38(FIG. 1) are fused together by flame singeing, as shown in FIG. 9,without closing or significantly reducing the size of the gasinlet/outlet openings.

A flame array like that shown in perspective view in FIG. 12 is used.The array is shown in FIG. 9 in a side elevation view to show thefeatures of each flame 124.

The flame 124 is a jet of burning gas moving downwardly in the directionof the arrows 128. The position and thrust of the jet are adjusted sothat just the bottom portion of the flame touches the upper edges 122 ofthe panel assembly as the assembly is moved past the flame array in thedirection of the arrow.

The dwell time of the flames on the panel edges is controlledempirically to limit the melting of the panel end to just enough to fusethe adjacent panel ends together without significantly closing the gaspassageways in the panels.

Other means can be used to fuse the ends and edges of the panelstogether, such as heated rollers and like devices.

The fused top and bottom walls 24 and 26, and the fused edges of thepanels at the inlet/outlet locations produce a strong heat-exchangerstructure which is capable of supporting itself without a separatehousing, thus saving substantial costs for sheet metal and sheet metalfabrication as compared with comparable prior heat-exchangers.

The heat-exchanger 20 is weather-resistant, highly corrosion-resistant,relatively easy to keep clean, and efficient, as well as beingrelatively economical to make.

Ventilation System

FIG. 12 is a partially-schematic side-elevation view of a ventilationsystem utilizing the heat-exchanger 20 of the invention to ventilate abuilding or other conditioned space 160.

As in my patent U.S. Pat. No. 6,176,305, a first fan 144 is positionedat the left inlet end 38 of the heat-exchanger to push outside air(“OSA”) through the heat-exchanger and out of the outlet 36 and into theconditioned space 160.

The outside air flows as indicated by the arrows 146 and 148 through anopening 149 in the wall 151 of a building and a fitting 147 secured tothe left end of the heat-exchanger, and out through another fitting 153secured to the right end of the heat-exchanger.

Curved fittings 154 and 156 fit over the angular extensions 28 and 32 ofthe heat-exchanger.

Mounted inside of outlet fitting 156 is a duct fan 142 which acts as asuction fan to pull exhaust air thorough inlet duct 154 and theheat-exchanger and expel the air through an exhaust outlet 155.

At the exhaust inlet end of the heat-exchanger is a motorized damper152, a water spray nozzle 150, and a porous mat 158 onto which the spraynozzle 150 sprays water to create evaporative cooling of the exhaustair, when needed.

In accordance with the present invention, either the fiberglass mat 158or the damper 152, or a combination of both is used to create arestriction to the inflow of exhaust air into the heat-exchanger.

Use of the damper 152 is preferred so as to minimize the restrictioncaused by the mat 158, especially when evaporative cooling is notrequired.

The exhaust fan 142 preferably is a centrifugal duct fan which occupiesthe full width of the duct 156 and is capable of creating a substantialpressure drop. The combination of this suction fan with the flowrestriction creates a significant pressure drop in the exhaust airentering the heat-exchanger. This is believed to significantly increasethe evaporation of water and, hence, the evaporative cooling of theexhaust air.

Another advantage of this ventilating system is that it providesresistance to the leakage of exhaust air into the incoming fresh airthrough any leaks which may exist in the heat-exchanger. This is becausethe exhaust air in the heat-exchanger is at a lower pressure than theoutside air, and any leaks would allow flow from the higher pressureconduits to the low pressure conduits, but not in the oppositedirection.

Thus, stale air is not allowed to mix to any significant degree with thefresh air coming into the conditioned space. Although this is highlydesirable in any residential or commercial building, it is especiallyadvantageous in hospitals or doctor's offices where it is important toprevent such mixing in order to prevent the spreading of pathogens.

Preferably, the heat-exchanger 20 is mounted with the right end slightlyhigher than the left so that the body of the heat-exchanger forms anangle θ of around 5 degrees with horizontal. This promotes drainage ofcondensate and excess water from the evaporative cooling system towardsthe left end 38.

A gutter 162 is provided in the duct 156 to catch the water drainingfrom the exhaust passageways of the heat-exchanger. The water gatheredthere flows through a line 168 to an optional waste water recoveryfacility (not shown) which returns the water for re-use in evaporativecooling, or elsewhere.

A float valve 164 is provided. It closes the drain system until thewater level in the tank of the valve 164 reaches a level sufficient toovercome the negative pressure of the fan 142. This prevents the drainfrom leaking air into the fitting 156 and reducing the effectiveness ofthe fan.

A similar gutter 166 and drain 170 are provided at the right end of theheat-exchanger, if needed. A similar gutter and drain can be provided atthe left end of the heat-exchanger, if needed.

The system shown in FIG. 12 preferably also has suitable control meansfor controlling the operation of the ventilator in heating, cooling andintermediate cooling modes, as described in my above-identified patentand pending patent application. Louvers, bypass ducts, de-icing means,etc., described there all can be used in the system of FIG. 12, asneeded or desired.

The above description of the invention is intended to be illustrativeand not limiting. Various changes or modifications in the embodimentsdescribed may occur to those skilled in the art. These can be madewithout departing from the spirit or scope of the invention.

1. A method of ventilating an enclosed space using an air handlingsystem including an isolating heat exchanger for conducting exhaust airform said enclosed space and outside air into said enclosed space andexchanging heat between said exhaust air and said outside air whileisolating the flows of said outside and exhaust air form one another, afirst fan to move said exhaust air through said heat exchanger, a secondfan to move said outside air through said heat exchanger, said first fanbeing located downstream from said heat exchanger in the flow path ofsaid exhaust air for pulling said exhaust air out of said heatexchanger, the steps of: (a) evporatively cooling said exhaust air at acooling location upstream of said heat exchanger in said flow path ofsaid exhaust air, and (b) creating a substantial air pressure dropbetween said first fan and said cooling location to augment saidevaporative cooling. 2-31. (canceled)
 32. A heat exchanger comprising,in combination, A plurality of panels of thermoplastic material, each ofsaid panels having two opposed broad surfaces and at least one edge,each of said broad surfaces having a greater surface area than saidedge, said panels each having at least one gas flow conduit structureforming at least one gas flow conduit, spaces between said panels, saidspacers forming at least a portion of one gas flow passageway betweeneach of a plurality of said panels, said spacers having edges alignedwith edges of said panels, said panels being assembled with said broadsurfaces of said panels parallel to one another and joined together bysaid spacers, said heat exchanger having a housing with at least onesolid integral side wall formed by said edges of said panels beingaligned with one another and fused together.
 33. A heat exchanger as inclaim 32 in which said panels and spacers form a body portion with fourintegral extensions extending therefrom and spaced from one another bysaid side wall and other side walls of like construction.
 34. A heatexchanger as in claim 32 in which said spacers are at least portions ofpanels shaped to form said passageways.
 35. A heat exchanger as in claim32 in which each of said panels comprise a plurality of elongated tubessecured together to form said panel, and said spacers are made ofthermoplastic material fused together with said edges of said panels.36. A heat exchanger as in claim 32 in which said extensions are shapedto mate with ductwork fittings for carrying air through said heatexchanger.
 37. A heat exchanger as in claim 32 in which said gas flowpassageways and gas flow conduits are positioned to conduct gases insubstantially opposite directions over a substantial portion of theirlengths.
 38. A heat exchanger as in claim 32 in which said integralhousing has at least one other solid integral side wall on the side ofsaid housing opposite the first-named side wall, said other side wallbeing formed by panel edges opposite the first-named edges aligned withone another and fused together.
 39. A heat exchanger comprising (a) aplurality of thermoplastic panels, each having a plurality of parallelconduits joined together side-by-side to form said panel, said panelhaving an edge, said panels being assembled together with their edgesbeing aligned with one another, (b) a plurality of spacers, each securedbetween adjacent ones of said panels and forming at least a portion of agas flow passageway between said adjacent panels, each of said spacershaving at least one edge aligned with said edge of one of said panels,(c) a housing having at least one solid integral wall formed by thealigned edges of said panels and said spacers fused together, (d) saidhousing sealing the edges of the spaces between said panels and theedges of said panels except in an inlet and an outlet area for saidconduits and an inlet and an outlet area for said gas flow passageways.40. A heat exchanger as in claim 39 in which each of said panels iselongated with a longitudinal axis and has two ends and an integralextension adjacent but spaced from each of said ends extendingtransversely to said longitudinal axis, and said housing covering thesides of said extension, said extensions being shaped to mate with andsecured to gas flow ductwork fittings, said ends of said panels formingtwo other extensions for mating with ductwork fittings.
 41. A heatexchanger as in claim 40 in which said housing covers said edges of saidpanels between adjacent ones of said extensions and isolates the flow ofgases through said conduits from the flow through said passageways. 42.A heat exchanger as in claim 41 in which the ends of said conduits ateach end of each of said panels is heat-welded to adjacent conduits andspacers.